I am study the heating process of a solid, which has several heating channels for hot fluid (gas or oil) flowing through. The hot fluid temperature changes little during the entire heating process. So the boundary condition at the channel wall belongs to the classical third-class:

-ks*dT/dn = HTC*(T-T_fluid)

where ks denotes the thermal conductivity of the solid, HTC denotes the heat exchange coefficient between hot fuid and solid depending on the fluid velocity, temperature, and thermal conductivity, etc. , T_fluid is the temperature of the hot fluid, and dT/dn and T are respectively the gradient and the value of the solid temperature at the boundary interface.

But I am still in a struggle with some warnings concerning the new variables Tref and HTC. Additionally I am not sure how to change the functions autoMap() and rmap().
Maybe someone can give me a hint.